scholarly journals $$\varLambda $$CDM suitably embedded in f(R) with a non-minimal coupling to matter

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
María Ortiz-Baños ◽  
Mariam Bouhmadi-López ◽  
Ruth Lazkoz ◽  
Vincenzo Salzano
Keyword(s):  
Energy Density ◽  
The Other ◽  
Accelerated Expansion ◽  
Gravitational Coupling ◽  
Minimal Coupling ◽  
Modified Theory Of Gravity ◽  
Expansion Of The Universe ◽  
The One ◽  
The Universe ◽  
Modified Theory

AbstractIn this work, we further study a metric modified theory of gravity which contains a non-minimal coupling to matter, more precisely, we assume two functions of the scalar curvature, $$f_1$$ f 1 and $$f_2$$ f 2 , where the first one generalises the Hilbert–Einstein action, while the second couples to the matter Lagrangian. On the one hand, assuming a $$\varLambda $$ Λ CDM background, we calculate analytical solutions for the functions $$f_1$$ f 1 and $$f_2$$ f 2 . We consider two setups: on the first one, we fix $$f_2$$ f 2 and compute $$f_1$$ f 1 and on the second one, we fix $$f_1$$ f 1 and compute $$f_2$$ f 2 . Moreover, we do the analysis for two different energy density contents, a matter dominated universe and a general perfect fluid with a constant equation of state fuelling the universe expansion. On the other hand, we complete our study by performing a cosmographic analysis for $$f_1$$ f 1 and $$f_2$$ f 2 . We conclude that the gravitational coupling to matter can drive the accelerated expansion of the universe.

Heuristic determination of the cosmological constant

2021 ◽  
pp. 2150114
Author(s):  
Manuel Urueña Palomo ◽  
Fernando Pérez Lara
Keyword(s):  
Field Theory ◽  
Energy Density ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Fundamental Constants ◽  
Quantum Field ◽  
Brute Force ◽  
Expansion Of The Universe ◽  
The Universe

The vacuum catastrophe results from the disagreement between the theoretical value of the energy density of the vacuum in quantum field theory and the estimated one observed in cosmology. In a similar attempt in which the ultraviolet catastrophe was solved, we search for the value of the cosmological constant by brute-force through computation. We explore combinations of the fundamental constants in physics performing a dimensional analysis, in search of an equation resulting in the measured energy density of the vacuum or cosmological constant that is assumed to cause the accelerated expansion of the universe.

scholarly journals Minimal extension of General Relativity: Alternative gravity model with non-minimal coupling between matter and curvature

2014 ◽  
Vol 11 (02) ◽  
pp. 1460003 ◽  
Author(s):  
Orfeu Bertolami ◽  
Jorge Páramos
Keyword(s):  
General Relativity ◽  
Lagrangian Density ◽  
Density Fluctuations ◽  
Accelerated Expansion ◽  
Minimal Extension ◽  
Minimal Coupling ◽  
Expansion Of The Universe ◽  
Scalar Theories ◽  
The Impact ◽  
The Universe

We examine an extension of General Relativity with an explicit non-minimal coupling between matter and curvature. The purpose of this work is to present an overview of the implications of the latter to various contexts, ranging from astrophysical matter distributions to a cosmological setting. Various results are discussed, including the impact of this non-minimal coupling on the choice of Lagrangian density, on a mechanism to mimic galactic and cluster dark matter, on the possibility of accounting for the accelerated expansion of the Universe, energy density fluctuations and modifications to post-inflationary reheating. The equivalence between a model exhibiting a non-minimal coupling and multi-scalar-theories is also discussed.

Time varying parameter in modified Chaplygin gas cosmology

2020 ◽  
Vol 35 (16) ◽  
pp. 2050128
Author(s):  
Koijam Manihar Singh ◽  
K. L. Mahanta ◽  
Longjam Parbati Devi ◽  
R. R. Sahoo
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Physical World ◽  
Chaplygin Gas ◽  
Accelerated Expansion ◽  
Interesting Phenomenon ◽  
Extra Energy ◽  
Time Varying Parameter ◽  
Expansion Of The Universe ◽  
The Universe

In the course of study of the evolution of the universe, it is seen that perhaps the extra energy generated and particles created due to the accelerated expansion of the universe might be absorbed by the dark energy and dark matter which are already existing in this universe. It is found that the energy density of dark energy can be expressed as a function of the energy density of the remaining matter portion of the universe which shows that the different components of the universe are correlated. According to the forms of the different types of interaction occurring between dark energy and the other different contents of the universe it may be possible to utilize the dark energy in different ways as it may take different forms of energy. As an interesting phenomenon, it is also observed that the concept of negative time may exist in this universe, and it may revolutionize some of the original concepts of nature and the physical world.

scholarly journals Cosmic accelerated expansion of the Universe with phantom fluid

2019 ◽  
Vol 97 (11) ◽  
pp. 1221-1224
Author(s):  
A.I. Keskin
Keyword(s):  
Source Term ◽  
The Other ◽  
Accelerated Expansion ◽  
Extended Version ◽  
Similar Form ◽  
Coincidence Problem ◽  
Expansion Of The Universe ◽  
Time Expansion ◽  
Phantom Phase ◽  
The Universe

The phantom behavior of the Universe is discussed in an extended version of Gauss–Bonnet gravity. Following the method proposed by the author (Int. J. Mod. Phys. D, 27, 1850078. 2018. doi: 10.1142/S0218271818500785 ), we obtain a viable cosmological model for the phantom phase of the Universe. We find a condition for m in the model ∼Gm, which shows phantom expansion of the Universe. On the other hand, using a phantom source term ∼T2n in the model we observe that the term ∼Gn, with n > 3/4, gives a phantomic space–time expansion. This form (Gn + T2n) obtained for the phantom phase of the Universe exhibits a similar form to Einstein’s gravity theory (R + Lm). However, we addressed the cosmic coincidence problem for the model.

scholarly journals FITTING THE LUMINOSITY DATA FROM TYPE Ia SUPERNOVAE IN THE FRAME OF THE COSMIC DEFECT THEORY

2009 ◽  
Vol 18 (03) ◽  
pp. 501-512
Author(s):  
A. TARTAGLIA ◽  
M. CAPONE ◽  
V. CARDONE ◽  
N. RADICELLA
Keyword(s):  
Accelerated Expansion ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The One ◽  
Ia Supernovae ◽  
The Universe ◽  
Good Agreement

The cosmic defect (CD) theory is reviewed and used to fit the data for the accelerated expansion of the universe, obtained from the apparent luminosity of 192 SnIa 's. The fit from the CD theory is compared with the one obtained by means of ΛCDM. The results from the two theories are in good agreement and the fits are satisfactory. The correspondence between the two approaches is discussed and interpreted.

scholarly journals Quantum relativistic cosmology: Dynamical interpretation and tunneling universe

2020 ◽  
pp. 2050123
Author(s):  
H. S. Vieira ◽  
V. B. Bezerra ◽  
C. R. Muniz ◽  
M. S. Cunha
Keyword(s):  
Asymptotic Behavior ◽  
Energy Density ◽  
Quantum Dynamics ◽  
Wave Functions ◽  
The Other ◽  
Relativistic Cosmology ◽  
Heun Functions ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Dynamical Interpretation

In this work, the wave functions associated to the quantum relativistic universe, which is described by the Wheeler–DeWitt equation, are obtained. Taking into account different kinds of energy density, namely, matter, radiation, vacuum, dark energy and quintessence, we discuss some aspects of the quantum dynamics. In all these cases, the wave functions of the quantum relativistic universe are given in terms of the triconfluent Heun functions. We investigate the expansion of the universe using these solutions and found that the asymptotic behavior for the scale factor is [Formula: see text] for whatever the form of energy density is. On the other hand, we analyze the behavior at early stages of the universe and found that [Formula: see text]. We also calculate and analyze the transmission coefficient through the effective potential barrier.

Cosmological constant

2018 ◽  
Author(s):  
Michael Kachelriess
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Vacuum Fluctuations ◽  
Present Epoch ◽  
Modify Gravity ◽  
Expansion Of The Universe ◽  
The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

scholarly journals Taxonomy of Dark Energy Models

Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 163
Author(s):  
Verónica Motta ◽  
Miguel A. García-Aspeitia ◽  
Alberto Hernández-Almada ◽  
Juan Magaña ◽  
Tomás Verdugo
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Energy Component ◽  
The Past ◽  
Energy Models ◽  
The Status ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Unknown Component

The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments with increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, faces several problems related to the nature of such energy component. This has led to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each model’s parameters using observational data. Finally, we summarize the status of dark energy modeling.

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